The loss of crest feathers can be due to the following:
- A bad molt. Northern Cardinals molt in late summer or early fall, after the breeding season is over. Sometimes the molting seems to go mad and they loose all or most of their crest feathers at once.
- The loss of all or most crest feathers at one time, can be caused by a bad infestation of mites. Preening tends to keep lice infestation down, but the top of the head may be more difficult to reach.
- Poor nutrition can cause feathers to fall out all at once.